An aircraft having a power unit supported in the airframe mounted configuration comprises an engine and a nacelle structure housing said engine. The nacelle structure comprises two displaceable parts called fan cowl doors or cowlings which can be opened on the ground during maintenance operations to access the various items of the power unit, the cowlings being closed and properly latched during operational conditions of the aircraft, therefore providing aerodynamic continuity for the power unit in flight.
The nacelle usually comprises at least one primary latch that fixes and latches the fan cowl doors during operation of the aircraft.
The indication of fan cowl doors not being properly latched is not a signal that is sent to the cockpit to avoid false open-door signals. For this reason, a visual inspection of the nacelle is necessary to detect if fan cowl doors are not properly latched.
The known procedures in the state of the art to detect if fan cowl doors are properly latched are based on the open primary latch visibility, as fan cowl doors in this position are flush with the other parts of the nacelle. When the primary latch is not closed, it must hang vertically. Moreover, and to improve latch visibility, the latch handle is painted with fluorescent colors.
The installation of the latches in the lower area of the fan cowls, their small size in comparison with the nacelle, and the location of the nacelle in some aircrafts, which is very close to the ground, make latch visual detectability very difficult.
Document U.S. Pat. No. 6,666,408 discloses a closure fault indicator for locking means interposed between two elements able to occupy with respect to one another an open position and a closed position, said indicator comprising retractable abutment means able to automatically maintain the two elements spaced from one another during the passage from the open position into the closed position. The indicator is arranged in such a way that the locking means can only be closed when the abutment means are retracted, preferably by a deliberate action on the part of an operator. The retractable abutment means maintaining the two elements open can be deactivated, so that the visual indication is lost, not being necessary for this deactivation to close the latches of the locking means, therefore being posed a problem of the aircraft being in a operating condition even though the locking means are not activated and the two elements are kept open.
Document U.S. Pat. No. 6,824,175 discloses a device for indicating incorrect closure of locking means consisting of a plurality of locking mechanisms located between two fan cowlings of an aircraft engine nacelle, this device including a body able to adopt, relative to the cowlings, a retracted position as well as a protruding position providing a warning of incorrect closure, this body in its retracted position being able to cover at least partially two of the locking mechanisms spaced along the longitudinal axis of the engine, said retracted position being exclusively authorized when each of the locking mechanisms that are able to be at least partially covered by the body is locked. The problem of such a device is that the design of the body of such a device has to be done taking into account both the tolerances of the fan cowlings and the aircraft engine, as well as the displacements and deformations of said fan cowlings, as said body adjusts on both cowlings. Moreover, as each type of aircraft engine needs a certain gap between the two fan cowlings when closed for providing an appropriate ventilation and drainage of the engine, the device of U.S. Pat. No. 6,824,175 has to be designed and adjusted so as to take this into account, therefore being its manufacture very complicated and leading to failures in the operating condition of the aircraft in which it is installed.
The present invention is oriented to the solution of the above-mentioned drawbacks.